Americans Can't Write?

I have been having a continuing problem when teaching Composition. The majority of college-level (freshmen) students have numerous grammatical errors in their papers. These are usually fragments and run-ons. How to spot and fix these errors should have been learned in elementary or junior high school. On top of that, a handful of students can not write at the sentence level. They have trouble writing coherent sentences, and, thus, can write only nonsensical papers. Needless to say, these students can not pass. Part of the problem has to do with placement: A student might be placed into the wrong class. Part of this problem could be that teachers in the public schools are 'passing on' students who clearly do not have the skills, and they keep getting 'passed on' all the way to college! Teachers do not want to be hassled by angry parents who may believe their child is a genius. It is well-known that parents have gotten their kid's grade(s) changed by appealing to the Principal (going around the teacher). What is going on? Teachers in K-12 have lost much of their authority. They are at the mercy of standardized tests, grade inflation, delusioned students, and delusional parents. When I was in public school in the 70's & 80's, you did not talk back to or challenge a teacher and his/her word. The grade you got was the one you deserved (Don't get me wrong: There were some exceptions.) Also, if you failed a course, you failed. Your parents did not go stomping into the school and create a scene and demand a grade change. Why can't students/parents/we accept that there are low, middle, and high achievers? There are dumb, middle, smart, super smart, and genius. That's it. It has always been, and always shall be.
Maybe school shouldn't be pushed as something for everyone? Or, high school needs to be as tough as it used to be, so that a high school diploma will, once again, be worth something. Then, those students for whom college is really not a good idea, will not feel compelled to go to college and waste their and everyone else's time. They can still get a good job with a high school diploma - IF the diploma had the clout that it used to! Of course, we can now go into a BLOG about what Higher Education is for? Do you go to college just to get a (supposedly) better job and higher income? Or do you go to learn and grow intellectually?